Residue-specific structures and membrane locations of pH-low insertion peptide by solid-state nuclear magnetic resonance.

Nicolas S Shu, Michael S Chung, Lan Yao, Ming An, Wei Qiang

Index: Nat. Commun. 6 , 7787, (2015)

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Abstract

The pH-low insertion peptide (pHLIP) binds to a membrane at pH 7.4 unstructured but folds across the bilayer as a transmembrane helix at pH∼6. Despite their promising applications as imaging probes and drug carriers that target cancer cells for cytoplasmic cargo delivery, the mechanism of pH modulation on pHLIP-membrane interactions has not been completely understood. Here, we show the first study on membrane-associated pHLIP using solid-state NMR spectroscopy. Data on residue-specific conformation and membrane location describe pHLIP in various surface-bound and membrane-inserted states at pH 7.4, 6.4 and 5.3. The critical membrane-adsorbed state is more complex than previously envisioned. At pH 6.4, for the major unstructured population, the peptide sinks deeper into the membrane in a state II' that is distinct from the adsorbed state II observed at pH 7.4, which may enable pHLIP to sense slight change in acidity even before insertion.